Automated analysis of low-molecular weight organic acids in ambient air by a microporous tube diffusion scrubber system coupled to ion chromatography

A method for the automatic analysis of low-molecular weight organic acids (C< 5) in the atmosphere was developed using a microporous tube coupled to an ion chromatograph. A 220 cm long microporous polytetrafluoroethylene (PTFE) tube provided high collection efficiencies of alkanoic acids (formic acid: 97%, acetic acid: 94%, propionic acid: 92%) and alkenoic acids (vinylacetic acid: 98% and methacrylic acid: 96%). A 20 min cycle analysis could be continuously repeated. The coefficient of variation for repeated measurements was less than 5% for concentrations higher than 1 ppbv and 5–10% for concentrations lower than 1 ppbv. The detection limits of formic acid, acetic acid and propionic acid were 0.20, 0.29 and 0.32 ppbv, respectively. The concentration in gas samples was calculated using a good linear gas-solution curve (calibration curve). Formic acid, acetic acid and propionic acid in the urban atmosphere were determined in the concentration range of 1.5–5.5, 1.0–2.8 and < 0.32–1.25 ppbv, respectively.